1. Field of the Invention
The present invention relates to, for example, an antenna device for a mobile communication terminal and a signal receiving method, and particularly to noise suppression techniques for an antenna.
2. Related Art
When a signal of digital terrestrial broadcasting, for example, is received with an antenna element contained in a mobile communication terminal such as a notebook personal computer (PC), noise produced in the terminal device itself may greatly affect reception characteristics of the antenna element. Some built-in, commercially available antenna devices for receiving digital terrestrial broadcasting have a low noise amplifier (LNA) inserted therein for compensating for a lowered gain due to the built-in structure. However, they suffer from a problem that the LNA also amplifies noise mixed with the signal and remain less effective. Further, an antenna element contained in a mobile communication terminal such as a notebook PC has problems of narrower bandwidth and lower gain of an antenna, for example.
As a technique for suppressing an undesired signal such as noise mixed therein, JP-A 2001-28561 (Kokai) describes providing a plurality of antenna elements, and using feedforward control through a multi-stage amplifying circuit and a phase circuit to cancel a signal received at each antenna element. However, this technique requires a plurality of amplifying circuits and phase circuits, and a circuit for controlling them, presenting a problem of a complex configuration.